26 August 2015 by Felicity
Restoring two of the most significant tide predicting machines ever built to their former working glory was a challenge recently undertaken by members of our conservation team. In this post, Steve Newman, head of metals conservation at National Museums Liverpool, talks us though the importance of the machines, which are now on display at the National Oceanographic Centre (NOC) on Brownlow Street, part of the University of Liverpool campus.
“Tide predicting machines were used in the late 19th and early 20th centuries to predict the ebb and flow of sea tides. Over the past ten months, we’ve restored the Doodson-Légé and Roberts-Légé tide predicting machines to working order.
Built in 1906, Roberts-Légé ‘Universal’ tide predicting machine was the second machine designed by Edward Roberts, a tidal scientist, who had originally worked for William Thomson, later Lord Kelvin, the designer of the first official tide prediction machine in 1872. The machine was manufactured by Légé & Co of London in 1906 and won the Grand Prix at the Franco-British Exhibition of 1908.
Arthur Doodson, head of the Proudman Tidal Institute, which was based at Bidston Observatory on the Wirral, purchased the Roberts-Légé machine in 1929. The revamped machine was then in service constantly through to the early 1960s when computers took over the calculations from tide tables.
Most notably, the Roberts-Légé machine was used by Arthur Doodson to calculate the tides along various points of the northern French coast that we used to plan the D-Day landings.
Each individual pulley wheel, that can be seen on the front of the machine, represents a different ‘constant’ or factor that creates tides. For example, the largest wheel represents the gravitation effects of the Moon on the tides but there are others for the distance of the Moon from Earth, the pull of the Sun and for the effects on tides of shallow water under-sea shelves and coastal drift. An extremely thin pure nickel tape passes around these pulley wheels and effectively sums up all their movements to provide tidal heights and mark the tidal highs and lows on a chart at the bottom of the machine.
The second machine that we’ve been working on is the Doodson-Légé tide predicting machine; the
second largest tide predicting machine ever built. This was a development from the earlier Roberts-Légé machine and designed by Arthur Doodson in the late 1940s and manufactured by Légé & Co. around 1948-49.
This much bigger machine was “easier” to set up and, after some additional mechanism added a few
years later, could calculate the high and low tide levels and their times at once – effectively halving the time it took on the older Roberts-Légé machine. It is estimated that, using the Doodson-Lége machine, it could take almost a month to calculate a year’s worth of tidal levels for a particular port and these were calculated a couple of years in advance. In comparison, it takes the computers used today a fraction of a second to do the same calculation to greater accuracy. Throughout the 1950s though, this machine was state-of-the-art.
The 1.8 ton Doodson-Légé and the 1.2 ton Roberts-Légé machines were recently transported to the NOC’s Joseph Proudman Building. The process took 5 ½ hours and required a large team of people. Staff at the NOC were in a jubilant mood watching the installation and cheered as the first machine to be lifted, the Roberts-Légé machine, touched down on the pavement beside the Proudman Building. The Doodson-Légé machine is a particularly symbolic object for them as it was at the heart of their tide prediction work for international ports from c1950 to the early 1960s.”
The two machines are on loan to the NOC as part of their new ‘Time & Tide’ exhibition, where the Doodson-Légé machine will be run monthly on open days.
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